Alarm circuit for fans

ABSTRACT

An alarm circuit is for a fan. The alarm circuit includes a direct current converting circuit, a first electronic switch, a second electronic switch, a clock chip, and a light emitting diode. When the fan does not operate, the light emitting diode blinks to warn the user that the fan may have a problem.

BACKGROUND

1. Technical Field

The present disclosure relates to an alarm circuit for a fan.

2. Description of Related Art

During operation of a computer, heat is generated by electricalcomponents of the computer. High-speed processing by data storagesystems results in a great amount of heat being generated. Thus, coolingof the data storage systems is an important consideration in designingcomputers. In a case that the fans in the data storage systems are notoperating, the data storage systems may be at risk.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the present embodiments can be better understood withreference to the following drawings. The components in the drawings arenot necessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the present embodiments.Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several views.

The FIGURE is a circuit diagram of an exemplary embodiment of an alarmcircuit for a fan.

DETAILED DESCRIPTION

The disclosure, including the accompanying drawings, is illustrated byway of example and not by way of limitation. It should be noted thatreferences to “an” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

Referring to the FIGURE, an alarm circuit is connected to a fan 1, tomonitor the fan 1, and warn users when the fan 1 is not operating. Thefan 1 includes a power pin VCC, a ground pin GND, and a speed pin Tach.The power pin VCC is connected to a first power supply +12V. The groundpin GND is grounded. The speed pin Tach is connected to the alarmcircuit.

An exemplary embodiment of the alarm circuit includes a diode D1, threetransistors Q1, Q2, and Q3, a clock chip U1, a light emitting diode(LED) D2, and a buzzer B.

An anode of the diode D1 is connected to the speed signal Tach of thefan 1. A cathode of the diode D1 is connected to a gate of thetransistor Q1 through three resistors R1, R2, and R3 in that order. Anode between the resistors R1 and R2 is grounded through a capacitor C1.A node between the resistors R2 and R3 is grounded through a capacitorC2. A node between the resistor R3 and the gate of the transistor Q1 isgrounded through a resistor R4.

A source of the transistor Q1 is grounded. A drain of the transistor Q1is connected to the first power supply +12V through a resistor R5. Thedrain of the transistor Q1 is further connected to a gate of thetransistor Q2. A source of the transistor Q2 is grounded through acapacitor C3. A drain of the transistor Q2 is connected to a secondpower supply +5V through a resistor R6.

The source of the transistor Q2 is further connected to a power pin VCCand a reset pin RESET of the clock chip U1. A trigger pin TRIG and athreshold pin THRES of the clock chip U1 are connected to the source ofthe transistor Q2 through resistors R7 and R8 in that order. The triggerpin TRIG and the threshold pin THRES of the clock chip U1 are alsogrounded through a capacitor C4. A control pin CONT of the clock chip U1is grounded through a capacitor C5. A discharge pin DISCH of the clockchip U1 is connected to a node between the resistors R7 and R8. A groundpin GND of the clock chip U1 is grounded. An output pin OUT of the clockchip U1 is connected to an anode of the LED D2 through a resistor R9. Acathode of the LED D2 is connected to a base of the transistor Q3. Anemitter of the transistor Q3 is grounded. A collector of the transistorQ3 is connected to a negative terminal of the buzzer B. A positiveterminal of the buzzer B is connected to the second power supply +5Vthrough a resistor R10.

When the fan 1 operates, the speed pin Tach of the fan 1 outputs pulsesignals. The pulse signals are converted to direct current voltages by adirect current converting circuit 2 which includes the resistor R2 andthe capacitor C2. At this time, the gate of the transistor Q1 receives ahigh level signal. The transistor Q1 is turned on. The transistor Q2 isturned off. As a result, the clock chip U1 cannot receive power to work.The LED D2 and the buzzer B are not activated.

When the fan 1 does not operate, the speed pin Tach of the fan 1 doesnot output pulse signal. At this time, the gate of the transistor Q1cannot receive a high level signal. The transistor Q1 is turned off. Thetransistor Q2 is turned on. As a result, the clock chip U1 is activated.At the same time, the second power supply +5V charges the capacitor C4through the resistors R8 and R7. According to the characteristic of theclock chip U1, when a voltage at the trigger pin TRIG of the clock chipU1 (namely a voltage at the capacitor C4) equals to two thirds of avoltage at the power pin VCC of the clock chip U1, the output pin OUT ofthe clock chip U1 outputs a low level signal. Moreover, the dischargepin of the clock chip U1 is turned on, the capacitor C4 dischargesthrough the resistor R7. When a voltage at the capacitor C4 equals to athird of the voltage at the power pin VCC of the clock chip U1, theoutput pin OUT of the clock chip U1 outputs a high level signal, and thedischarge pin of the clock chip U1 is turned off. In this way, the clockchip U1 outputs periodic pulse signals.

When the output pin OUT of the clock chip U1 outputs a high levelsignal, the LED D2 is activated. The transistor Q3 is turned on. As aresult, the buzzer B is activated. When the output pin OUT of the clockchip U1 outputs a low level signal, the LED D2 is not activated. Thetransistor Q3 is turned off. As a result, the buzzer B is not activated.In this way, the LED D2 blinks, and the buzzer B sounds alternately, towarn the user that the fan 1 may have a problem. In the embodiment, afrequency of the LED D2 blinking and a frequency of the buzzer Bsounding can be decided by resistances of the resistors R7 and R8, andcapacitance of the capacitor C4.

The foregoing description of the exemplary embodiments of the disclosurehas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the disclosure to theprecise forms disclosed. Many modifications and variations are possiblein light of the above everything. The embodiments were chosen anddescribed in order to explain the principles of the disclosure and theirpractical application so as to enable others of ordinary skill in theart to utilize the disclosure and various embodiments and with variousmodifications as are suited to the particular use contemplated.Alternative embodiments will become apparent to those of ordinary skillsin the art to which the present disclosure pertains without departingfrom its spirit and scope. Accordingly, the scope of the presentdisclosure is defined by the appended claims rather than the foregoingdescription and the exemplary embodiments described therein.

What is claimed is:
 1. An alarm circuit for a fan, the alarm circuitcomprising: a direct current converting circuit comprising an inputconnected to a speed pin of the fan, wherein the direct currentconverting circuit converts pulse signals from the speed pin of the fanto a direct current voltage when the fan operates; a first electronicswitch comprising a first terminal connected to an output of the directcurrent converting circuit, a second terminal grounded, and a thirdterminal connected to a first power supply, wherein the first electronicswitch is turned on when the first terminal of the first electronicswitch receives the direct current voltage from the direct currentconverting circuit; a second electronic switch comprising a firstterminal connected to the third terminal of the first electronic switch,a second terminal grounded, and a third terminal connected to a secondpower supply, wherein the second electronic switch is turned off whenthe first electronic switch is turned on; a clock chip comprising apower pin connected to the second terminal of the second electronicswitch, a reset pin connected to the second terminal of the secondelectronic switch, a trigger terminal connected to the second terminalof the second electronic switch through a first resistor and a secondresistor in series and grounded through a first capacitor, a thresholdpin connected to the second terminal of the second electronic switchthrough the first and second resistors in series and grounded throughthe first capacitor, and a discharge pin connected to a node between thefirst and second resistors; and a light emitting diode comprising ananode connected to an output pin of the clock chip, and a cathodegrounded.
 2. The alarm circuit of claim 1, wherein the first electronicswitch is a transistor, a gate of the transistor is the first terminalof the first electronic switch, a source of the transistor is the secondterminal of the first electronic switch, a drain of the transistor isthe third terminal of the first electronic switch.
 3. The alarm circuitof claim 1, wherein the second electronic switch is a transistor, a gateof the transistor is the first terminal of the second electronic switch,a source of the transistor is the second terminal of the secondelectronic switch, a drain of the transistor is the third terminal ofthe second electronic switch.
 4. The alarm circuit of claim 1, whereinthe direct current converting circuit comprises a third resistor and asecond capacitor, a first terminal of the third resistor functions asthe input of the direct current converting circuit, a second terminal ofthe third resistor functions as the output of the direct currentconverting circuit, the second terminal of the third resistor is furthergrounded through the second capacitor.
 5. The alarm circuit of claim 1,further comprising a diode and a third resistor, wherein an anode of thediode is connected to the speed pin of the fan, a cathode of the diodeis connected to the input of the direct current converting circuitthrough the third resistor.
 6. The alarm circuit of claim 1, furthercomprising: a third electronic switch comprising a first terminalconnected to the cathode of the light emitting diode, a second terminalgrounded, and a third terminal, wherein the third electronic switch isturned on when the light emitting diode is turned on; and a buzzercomprising a positive terminal connected to the second power supply, anda negative terminal connected to the third terminal of the thirdelectronic switch.
 7. The alarm circuit of claim 6, wherein the thirdelectronic switch is a transistor, a base of the transistor is the firstterminal of the third electronic switch, an emitter of the transistor isthe second terminal of the third electronic switch, a collector of thetransistor is the third terminal of the third electronic switch.